Metal-ceramic substrate for electric circuits or modules, method for producing one such substrate and module comprising one such substrate

ABSTRACT

The invention relates to a metal-ceramic substrate for electric circuits or modules, said substrate comprising a ceramic layer which is provided with at least one metallic layer of a first type applied to a surface of said ceramic layer in a plane manner. An insulating layer consisting of a glass-containing material is applied to at least one partial region of a surface of the metallic layer of the first type, said surface opposing the ceramic layer, and a metallic layer of a second type is applied to the insulating layer, the insulating layer and the metallic layer of a second type respectively being thinner then the ceramic layer and the metallic layer of the first type.

The invention relates to a metal-ceramic substrate according to thepreamble of claim 1 or 15, to a method for producing one suchmetal-ceramic substrate according to the preamble of claim 17 and amodule, particularly a semiconductor power module with a metal-ceramicsubstrate according to the preamble of claim 27.

Metal-ceramic substrates, also copper-ceramic substrates for electriccircuits, particularly for semiconductor power circuits or modules, areknown in a wide variety of designs. Also known in particular for themanufacture of strip conductors, connectors, etc. is the application ofa metallization on a ceramic, e.g. on an aluminum-oxide ceramic by meansof the so-called “DCB process” (direct copper bond technology), saidmetallization being formed from metal or copper foils or metal or coppersheets, the surfaces of which comprise a layer or a coat (hot-meltlayer) from a chemical bond between the metal and a reactive gas,preferably oxygen. In this method, which is described for example inU.S. Pat. No. 3,744,120 and in U.S. Pat. No. 2,319,854, this layer orcoat (hot-melt layer) forms a eutectic with a melting temperature belowthe melting temperature of the metal (e.g. copper), so that the layerscan be bonded to each other by placing the foil on the ceramic andheating all layers, namely by melting the metal or copper essentiallyonly in the area of the hot-melt layer or oxide layer.

This DCB process then comprises, for example, the following processsteps:

-   a) oxidation of a copper foil so as to produce an even copper oxide    layer;-   b) placing the copper foil on the ceramic layer;-   c) heating the composite to a process temperature between approx.    1025 and 1083° C., e.g. to approx. 1071° C.;-   d) cooling to room temperature.

Electric circuits or modules, particularly power circuits or moduleswith a power element and a control or drive element have heretofore beenmanufactured in the manner that a metal-ceramic substrate is used as asubstrate or circuit board for the power element and that the control ordrive circuit on a separate circuit board assembled with its componentsis then mounted by suitable means in a second level above the powerelement or next to the latter on the metal-ceramic substrate.

The disadvantage of this method, for example, is the high cost ofmanufacture, since the power element and the control or drive stage mustbe manufactured separately and then connected and bonded together inproduction. In particular, this known technology does not allow themultiple manufacture of the entire module (power element+control anddriver stage) in accordance with the principles of efficient production.

The object of the invention is to present a metal-ceramic substratewhich enables the particularly efficient production of circuits,particularly semiconductor circuits and especially power circuits with acorresponding control and driver stage.

This object is achieved by a metal-ceramic substrate according to claim1 or 15. A method for producing this substrate is embodied according toclaim 17. A semiconductor module is embodied according to claim 27.

Further embodiments of the invention are the subject of the dependantclaims.

The essential advantages of the invention can be summarized as follows:

-   e) simplified production of both the power area and the control and    driver area;-   f) exact positioning of the power area and of the control or drive    area and the areas formed there by means of structuring (strip    conductors, contact surfaces, mounting surfaces, etc.) and therefore    also simplification of the mounting of the components;-   g) mounting of elements in the power area and of the control and    driver area is possible in one step;-   h) since no organic substrate material is used, high soldering    temperatures, for example soldering temperatures up to 400° C. for    mounting of the components are possible, and in particular,    lead-free solder can be used;-   i) application of a solder or adhesive paste during surface mounting    of the substrate is simplified considerably, since the level of the    surface of the power element to be mounted and the level of the    surface of the control or driver element to be mounted differ only    minimally;-   j) the application of solder paste or adhesives for surface mounting    of both the power element and the control or drive element is    possible in one step;-   k) simplified wiring between the power element and the control and    driver element through ultrasonic bonding;-   l) improved cooling of the control or drive stage due to improved    bonding to a cooling system;-   m) highly complex lay out of the control and driver stage is    possible due to cross-over technology, which can easily be    implemented.

Exemplary embodiments of the invention are explained below in moredetail with reference to the drawings, wherein:

FIGS. 1 and 2 show a simplified cross section of semiconductor modulesaccording to the state of the art;

FIG. 3 shows a schematic representation of the layer construction of oneembodiment of the metal-ceramic substrate according to the invention;

FIG. 4 shows a cross section of a metal-ceramic substrate of FIG. 3,structured with an area for holding at least one power semiconductorcomponent and a further area for a control circuit;

FIGS. 5 and 6 show a schematic representation of the layer constructionof further embodiments of the metal-ceramic substrate according to theinvention;

FIG. 7 shows a cross section of a semiconductor module manufacturedusing the structured metal-ceramic substrate of FIG. 4;

FIG. 8 shows the semiconductor module of FIG. 7, however together withan additional base plate;

FIG. 9 shows a partial representation of a semiconductor modulemanufactured using the structured metal-ceramic substrate of FIG. 5;

FIG. 10 shows a simplified representation in top view of a furtherpossible embodiment of the metal-ceramic substrate according to theinvention.

FIG. 1 shows a simplified representation in cross section of asemiconductor module 1, as known from the prior art. This semiconductormodule consists of a copper-ceramic substrate 2 with semiconductor powercomponents 3 and 4, for example transistors or thyristors forcontrolling an electric drive, etc., and of a printed circuit board 5made of organic material (plastic), which is equipped with components 6and forms a driver or control stage to control the power components 3and 4. The printed circuit board 5 with the components 6 is locatedabove the substrate 2. FIG. 2 shows a semiconductor module 1 a, also asknown from the prior art. The substrate 2 with the power components 3and 4 is provided on a common base plate 7, together with the printedcircuit board 5 made of organic material (plastic) and comprising thecomponents 6 and located to the side of the substrate 2 on a carrier 7.

The known construction has the disadvantage of complex wiring andensuing higher assembly costs. In addition, it is necessary for bothparts of the module 1 or 1 a, namely the substrate 2 and the partcomprising the printed circuit board 5 with the components 6 to bemanufactured separately, and then connected and mechanically bonded.

FIG. 3 shows the general layer construction of a metal-ceramic substrate10 according to the invention. This substrate consists of the ceramiclayer 11, which is provided on each side with a metallic layer 12 and 13of a first type. In the depicted embodiment, the metallic layers 12 and13 are formed from metallic foils, which are applied in a plane mannerto the surface of the ceramic layer 11 by means of the direct bondingprocess.

A layer 14 made of a dielectric or insulating material is applied to theupper metallic layer 12 in FIG. 3, the insulating layer having athickness that is considerably less than the thickness of the metalliclayers 12 and 13. The layer 14 is made for example of a glass-containingmaterial, which is applied to the metallic layer 12 by means of heatingor baking. A second metallic layer 15 of a second type is provided onthe insulating layer 14. The metallic layer 15 is manufactured byapplying a conductive paste and by baking this paste, likewise with athickness that is considerably less than the thickness of the metalliclayers 12 and 13.

The thickness of the ceramic layer 11 is, for example, 0.2 to 2 mm. Themetallic layers 12 and 13 have a thickness, for example, between 0.1 and0.9 mm. The insulating layer 14 has a thickness between 0.015 and 0.15mm. The thickness of the metallic layer 15 is between approx. 0.015 and0.15 mm.

In the depicted embodiment, the metallic layers 12 and 13 have the samethickness and are made of copper. The ceramic of the ceramic layer 11is, for example, an aluminum oxide ceramic.

The multi-layer metal-ceramic substrate is manufactured for example in aprocess with the following process steps:

-   a) To form the metallic layers 12 and 13, at least two blanks of a    copper foil oxidized on their surfaces are applied to one surface of    the ceramic layer 11 by means of the DCB process. Before this    application, the copper foil blanks are tempered, preferably in a    preceding step, in a protective gas atmosphere, for example in a    nitrogen atmosphere, for the purpose of reducing the hardness of the    copper material.-   a) After cooling, a layer made of a glass-containing paste forming    the later insulating layer 14 is applied to the metallic layer 12 by    means of pressing or some other suitable method.-   b) The paste is dried and then baked on at a temperature below the    temperature of the DCB process, i.e. at a temperature between 750    and 1030° C., so that the paste then forms the insulating layer 14    adhering to the metallic layer 12.-   c) After cooling again, a conductive paste containing metallic    constituents is applied to the insulating layer 15, likewise for    example by pressing or some other suitable process.-   d) The conductive paste (thick film) is then baked on at a    temperature between 750 and 1030° C.

In order to achieve a greater thickness for the insulating layer 14and/or the metallic layer 15, the process steps b) and c) and/or d) ande) can be repeated one or more times. Generally it is also possible toapply at least one further layer consisting of at least the insulatinglayer 14 and one further metallic layer 15 to the metallic layer 15. Theoxidation of the copper foil blanks can take place before and/or aftertempering and also during the DCB process.

For the insulating layer 14, a paste is preferably used that afterbaking produces a layer 14 with a higher melting point than the pastebefore baking, so that repeated application and baking of theglass-containing paste is possible in order to achieve a thicker layer.The same applies to the paste used for the metallic layer 15. A suitablepaste for manufacturing the insulating layer 14 is, for example, thepaste “Dielectric Composition 4575D” available from Du Pont Electronics.A suitable paste for manufacturing the metallic layer 15 is, forexample, the paste “Copper Conductor Composition 9922” also availablefrom Du Pont Electronics.

For the explanation of the general layer construction and of possiblemanufacturing processes, it was assumed above that the composite layerconsisting of the insulating layer 14 and the metallic layer 15 coversthe metallic layer 12 over its entire surface. In practical applicationsof the substrate according to the invention, the application of thecomposite layer(s) 14/15 takes place in a manner that said compositelayer(s) cover only a partial area of the surface of the metallic layer12, as indicated in FIG. 4 in the section I of the metal-ceramicsubstrate 10 a there, while in section II the surface of the metalliclayer 12 is exposed. This makes it possible to structure the metalliclayer 12 using a suitable technology, for example etch-maskingtechnology, for the purpose of forming conductor strips, contactsurfaces, etc. as indicated in FIG. 4 by 12′. In the same manner, themetallic layer 15 is also structured to form conductor strips, contactsurfaces, etc. as indicated by 15′. The structuring of the metalliclayer 15 is much finer than the structuring of the metallic layer 12,which is possible simply due to the considerably lower thickness of themetallic layer 15.

The structuring of the metallic layer 15 takes place for examplelikewise by means of etch-masking technology and/or already by thestructured application of the conductive paste forming the metalliclayer 15, for example by structured pressing.

If the metallic layer 15 is structured with an etch-masking process,which is to take place after the structuring of the metallic layer 12,it is generally not necessary to cover the structured metallic layer 12or its areas 12′ with an etch-resistant mask. Since the thickness of themetallic layer 15 is much lower than the thickness of the metallic layer12, an additional reaction of the etching medium during structuring ofthe metallic layer 15 has no effect on the metallic layer 12. At most,this would cause the edges of the structured areas 12′ to be rounded,with the positive effect of preventing sharp edges and increasing theelectric strength.

The use of the direct bonding process for applying the metallic layers12 and 13 achieves a high bonding strength (peel strength) greater than30 N/cm for these metallic layers on the ceramic layer 11. This highbonding strength is essential in order to prevent peeling or detachmentof the metallic layer 12, particularly on the edge of the metallic layer12 or the structured areas 12′, such peeling or detachment resultingfrom thermal tensions after cooling of the insulating layer 14 and/or ofthe metallic layer 15, after they are baked on respectively.

FIG. 5 shows as a further possible embodiment a metal-ceramic substrate10 b, which differs from the substrate 10 a essentially only in that theinsulating layer 14 is located in a trough-like recess 16 of astructured area 12′ of the metallic layer 12. In deviation from themethod described above for manufacturing the metal-ceramic substrate 10,the substrate 10 b is manufactured for example so that after applicationof the metallic layers 12 and 13 by means of direct bonding (processstep a)), in one or more subsequent process steps, for example by meansof an etch-masking process, first the trough-shaped recess 16 is formedin the metallic layer 12, without further structuring of the metalliclayer 12. Only then is the insulating layer 14 formed in the recess 16in the further process steps b) and c), which again can be repeated oneor more times, and then the metallic layer 15 is applied in processsteps d) and e), which also can be repeated. In further process steps,the metallic layers 12 and 15 are structured, for example likewise withetch-masking technology, in order to form the structured areas 12′ and15′. One structured area 12′ then comprises the recess 16 with theinsulating layer 14. The remaining structured areas 12′ form for examplecontact surfaces, conductor strips, etc. for the semiconductor powercomponent(s).

The metallic layer 15 in the depicted embodiment is structured so thatall areas 15′ are electrically insulated by means of the insulating area14 from the area 12′ comprising the recess 16. At least some of theareas 15′ form conductor strips, contact surfaces, etc. for the lowpower control circuit.

Of course, other processes are also conceivable for manufacturing themetal-ceramic substrate 10 b, e.g. such processes in which duringcreation of the recess 16 or in a preceding or subsequent process step,the structuring of the metallic layer for forming the areas 12′ and/orthe structured areas 15′ of the metallic layer takes place by means ofstructured application of the paste forming the metallic layer.

The metal-ceramic substrate 10 b with the recess 16 features theadvantage that the application of the insulating layer 14 is simplifiedand also that the top of this insulating layer is located in one planewith the top of the metallic layer 12 or the areas 12′, which isespecially advantageous for the manufacturing process, particularly forthe further processing of this substrate.

This embodiment also makes it possible to apply the insulating layer 14so that the top of the area 12′ comprising the recess 16 is reliablykept free of the material forming the insulating layer 14, resulting ina purely metallic surface outside of the insulating layer 14 on the topof the area 12′ comprising the recess 16, on which (metallic surface)additional elements, such as a housing, can be hermetically fastenede.g. by means of soldering or some other means, without hindrance fromremainders of the material forming the insulating layer 14.

FIG. 6 shows as a further possible embodiment a partial section of thelayer construction of a metal-ceramic substrate 10 c, which differs fromthe substrate 10 in that after structuring of the metallic layer 15, afurther insulating layer 14 is applied to this metallic layer or to itsstructured areas 15′, likewise by application of the glass-containingpaste and baking of the paste after drying.

During application of the additional insulating layer 14 c, openings orwindows are provided in this layer, above several of the structuredareas 15′, so that during application of the additional metallic layer15 c, which corresponds to the metallic layer 15 and which likewise isproduced by application and baking of the conductive paste, anelectrical connection between the structured areas 15′ and theadditional metallic layer 15 c above these areas exists. Of course, itis also possible to apply additional composite layers, consisting of atleast one insulating layer corresponding to the insulating layer 14 or14 c and at least one metallic layer corresponding to the metallic layer15 or 15 c, on the metallic layer 15 c, preferably after structuring ofthis metallic layer. The construction depicted in FIG. 6 can thereforebe used to achieve very complex metal-ceramic substrates or substrateareas for circuits with reduced power, particularly for control circuitsfor electric power components, with a small overall size.

FIG. 7 shows a simplified representation in cross section of asemiconductor module 17, which is manufactured using the metal-ceramicsubstrate 10 a. One semiconductor component 3 or 4 is providedrespectively on section II of the substrate 10 a and on two structuredareas 12′ located there. By means of electrical connections 18 (e.g.wire bonds) the components 3 and 4 are connected with additional areas12′, which serve as contact surfaces and on which external powerconnections 19 are provided.

The structured areas 15′ form the conductor strips, contact surfaces,etc. for the control circuit or driver for controlling the power stagecomprising the components 3 and 4. The corresponding components 6 ofthis driver stage are provided on the areas 15′. Additional areas 15′form contact surfaces, which are connected by means of internalconnections 20 with the components, conductor strips, etc. and whichthen for example also form external control connections for the module17, in addition to contact surfaces, which are connected by means ofinternal connections 21 with the power element II.

FIG. 8 again shows the power module 17, together with a base plate 22made of a material having high heat conductivity and high mechanicalstability. Especially with large, complex modules, this base plate 22 isuseful for increasing the mechanical and/or thermal stability and alsofor preventing deformation of the metal-ceramic substrate 10 a in caseof fluctuations in temperature, etc.

Instead of the substrate 10 a, another metal-ceramic substrate accordingto the invention can be used for the power module, for example thesubstrate 10 b or 10 c, i.e. a substrate with the construction depictedin FIGS. 5 and 6. FIG. 9 shows a module 17 a with the substrate 10 b.

Copper is a suitable metal for the metallic layers, particularly alsofor the metallic layers 12 and 13, whereby the metallic layers 12 and 13are then manufactured using copper foils and using the direct copperbonding technology. The use of other metals is also generally possible.

A suitable ceramic for the ceramic layer 11 is, for example, an aluminumoxide ceramic (Al₂O₃). Other ceramics are also conceivable, for exampleAlN, BeO, CBN, Si₃N₄ and SiC.

In the method described above in connection with FIG. 3 it was assumedthat the metal or conductive paste (thick film paste) forming themetallic layer is either applied in an unstructured state and then bakedon, after which structuring takes place by means of a suitable method,e.g. an etch-masking method, for producing the areas 15′, or theconductive paste is already applied with the desired structuring andbaked on. It is also possible to use a photo-sensitive conductive paste,i.e. a conductive paste, which after being applied and before beingbaked on is exposed corresponding to the desired structure, whereby thenfor example the non-exposed areas are removed in a subsequent processstep (“developing process”), in order to achieve a very fine structuringbefore the conductive paste is baked on. The photo-sensitive conductivepaste can also be designed so that after exposure, the exposed areas canbe removed.

A method for producing the metal-ceramic substrate would then comprisethe following process steps when using the photo-sensitive conductivepaste:

-   a) a) To form the metallic layers 12 and 13, at least two blanks of    a copper foil oxidized on their surfaces are applied to one surface    of the ceramic layer 11 by means of the DCB process. Before this    application, the copper foil blanks are tempered, preferably in a    preceding step, in a protective gas atmosphere, for example in a    nitrogen atmosphere, for the purpose of reducing the hardness of the    copper material.-   b) After cooling, a layer made of a glass-containing paste forming    the later insulating layer 14 is applied to the metallic layer 12 by    means of pressing or some other suitable method.-   c) The paste is dried and then baked on at a temperature below the    temperature of the DCB process, i.e. at a temperature between 750    and 1030° C., so that the paste then forms the insulating layer 14    adhering to the metallic layer 12.-   d1) Afterwards, a layer consisting of the photo-sensitive conductive    paste is applied and this layer is exposed corresponding to the    desired structure.-   d2) In a subsequent process step, the exposed or non-exposed areas    are removed from the layer formed by the paste.-   e) The structured conductive paste (thick film) is then baked on at    a temperature between 750 and 1030° C.

The structuring of the metallic layer 12 takes place in this process forexample before the application of the insulating layer 14, i.e.following the above process step a).

FIG. 10 shows a simplified partial representation in top view of ametal-ceramic substrate 10 d with the structured areas 12′ formed by themetallic layer 12. Several areas 12′ in the depicted embodiment areprovided on their edge with a frame-like solder stop application 23,which is formed from a layer consisting of the conductive paste, e.g.“Dielectric Composition 4575D” applied to the exposed top of the areas12′, as used above for the insulating layer 14. This layer 23 has beenproven to provide an optimum solder stop, i.e. it effectively preventssolder from flowing over this solder stop to adjacent areas 12′ duringsoldering of components, connections, etc. to areas provided with thesolder stop, thus preventing unwanted electrical connections. Eachsolder stop application 23 encloses the part of the structured area 12′on which (part) solder is later applied. Due to the material used(glass-containing paste), the respective solder stop application 23 hasa high degree of heat resistance, which in turn allows the use ofsolders with high processing temperatures, particularly also lead-freesolders.

The substrate 10 d is manufactured in the manner that after applicationof the metallic layer 12 and also of the metallic layer 13, ifapplicable, to the ceramic layer 11 by means of the direct bondingprocess and after structuring of the metallic layer 12, theglass-containing paste is applied corresponding to the desired flow ofthe respective solder stop application 23 to areas 12′, namely with athickness of approximately 0.015-0.15 mm. After the paste dries, it isbaked on at a temperature between 750 and 1030° C.

If at least one insulating layer 14 is applied to the substrate 10 d,then the application, drying and baking of the glass-containing pastefor the insulating layer 14 and the respective solder stop application23 takes place in common steps.

The invention was described above based on exemplary embodiments. Itgoes without saying that numerous modifications and variations arepossible without abandoning the underlying inventive idea upon which theinvention is based.

REFERENCE NUMBERS

-   1, 1 a semiconductor power module according to the state of the art-   2 metal-ceramic substrate-   3, 4 semiconductor power components-   5 additional printed circuit board-   6 components of a control or driver stage-   7 base plate-   10, 10 a, 10 b metal-ceramic substrate according to the invention-   10 c, 10 d metal-ceramic substrate according to the invention-   11 ceramic layer-   12, 13 metallic layer-   12′ structured area-   14 c insulating layer-   15 c additional metallic layer-   15′ structured area-   16 recess-   17, 17 a power module according to the invention-   18 internal connection-   19 external power connection-   20, 21 internal connection-   22 base plate-   23 solder stop application

1. Metal-ceramic substrate for electric circuits or modules,particularly for such circuits or modules with at least one powerelement or component (II) and with at least one low-power crcuitelement, with at least one ceramic layer having a thickness between0.2-2 mm, with at least one metallic layer (12, 13) of a first typeapplied in a plane manner to the surface of the ceramic layer and with athickness between 0.1 and 0.9 mm, characterized in that an insulatinglayer (14) made of a glass-containing material with a thickness ofapproximately 0.015-0.15 mm is applied to at least one partial area ofthe surface of the at least one metallic layer (12) of the first typeopposing the ceramic layer (11) and that at least one metallic layer(15) of a second type with a thickness between 0.015-0.15 mm is appliedto this insulating layer.
 2. Substrate according to claim 1,characterized in that the at least one metallic layer (12) of the firsttype or structured areas (12′) of this metallic layer form at least onepower area for arranging power components (4, 5), and that the at leastone metallic layer (15) of the second type forms at least one control ordriving area of the substrate on one exposed area or on structured areas(15′) of this metallic layer (15).
 3. Substrate according to claim 2,characterized in that several composite layers consisting of theinsulating layer (14, 14 c) and the metallic layer (15, 15 c) of thesecond type are provide at least on one partial area of the at least onemetallization (12) of the first type.
 4. Metal-ceramic substrate forelectric circuits or modules, particularly for such circuits or moduleswith at least one power element or component (II) and with at least onelow-power crcuit element, with at least one ceramic layer having athickness between 0.2-2 mm, with at least one metallic layer (12, 13) ofa first type applied in a plane manner to the surface of the ceramiclayer and with a thickness between 0.1 and 0.9 mm, characterized in thatan insulating layer (14) made of a glass-containing material with athickness of approximately 0.015-0.15 mm is applied to at least onepartial area of the surface of the at least one metallic layer (12) ofthe first type opposing the ceramic layer (11) and that at least onemetallic layer (15) of a second type with a thickness between 0.015-0.15mm is applied to this insulating layer.
 5. Substrate according to claim1, characterized in that the at least one metallic layer (12) of thefirst type or structured areas (12′) of this metallic layer form atleast one power area for arranging power components (4, 5), and that theat least one metallic layer (15) of the second type forms at least onecontrol or driving area of the substrate on one exposed area or onstructured areas (15′) of this metallic layer (15).
 6. Substrateaccording to claim 2, characterized in that several composite layersconsisting of the insulating layer (14, 14 c) and the metallic layer(15, 15 c) of the second type are provide at least on one partial areaof the at least one metallization (12) of the first type.
 7. Substrateaccording to one of the foregoing claims, characterized in that theinsulating layer (14) is provided in a recess (16) of an underlyinglayer, for example in a recess (16) of the one metallic layer (12) ofthe first type.
 8. Substrate according to claim 4, characterized in thatthe recess has a depth between approximately 0.015 and 0.15 mm. 9.Substrate according to one of the foregoing claims, characterized inthat one metallic layer (12, 13) of the first type is applied to eachsurface of the at least one ceramic layer (11).
 10. Substrate accordingto claim 6, characterized in that the at least one insulating layer (14)with the additional metallic layer (15) of the second type and/or thecomposite layer formed by several insulating layers (14, 14 c) and/orseveral metallic layers (15, 15′) of the second type are provided onlyon one of the two metallic layers of the first type.
 11. Substrateaccording to one of the foregoing claims, characterized in that the atleast one metallic layer (12, 13) of the first type is applied to theceramic layer with a peel strength greater than 30 Ncm.
 12. Substrateaccording to one of the foregoing claims, characterized in that thethermal expansion coefficient of the at least one metallic layer (12,13) of the first type in the plane of the substrate, i.e. parallel tothe top of the substrate, is less than 10 ppm.
 10. Substrate accordingto one of the foregoing claims, characterized in that the metal of theat least one metallic layer of the first type is copper.
 11. Substrateaccording to one of the foregoing claims, characterized in that the atleast one metallic layer (12, 13) of the first type is formed from ametal foil, for example copper foil, which is attached by means of thedirect bonding process to the ceramic layer.
 12. Substrate according toone of the foregoing claims, characterized in that the at least oneadditional metallic layer (15, 15 c) of the second type is producedusing a conductive paste.
 13. Substrate according to one of theforegoing claims, characterized in that at least one structured area(12′), preferably a structured area of the at least one metallic layerof the first type is provided with a solder stop application consistingof a glass-containing material.
 14. Substrate according to claim 13,characterized in that the solder stop application (23) is produced byapplication and baking of a glass-containing paste.
 15. Metal-ceramicsubstrate for electric circuits or modules, with at least one ceramiclayer and with at least one metallic layer (12) applied in a planemanner to one surface of the ceramic layer, which (metallic layer) isstructured in order to form strip conductors, contact surfaces, mountingsurfaces, etc., characterized in that a solder stop application (23)made of a glass-containing material is provided on at least onestructured area (12′) of the metallic layer (12).
 16. Substrateaccording to claim 15, characterized in that the solder stop application(23) has a thickness of approximately 0.015 to 0.15 mm.
 17. Method forproducing a metal-ceramic substrate, in which a metallic foil, forexample a copper foil, is attached by means of the direct bondingprocess on at least one surface of a ceramic layer in order to form ametallic layer of a first type, characterized in that a glass-containingpaste is applied to at least one partial area of the metallic layer (12)of the first type in order to form an insulating layer, and then driedand baked on at a temperature between 750 and 1030° C., and that anadditional metallic layer (15, 15 c) of a second type is produced on theinsulating layer (14, 14 c) by applying and baking on a paste(conductive paste) comprising metallic constituents at a temperaturebetween 750 and 1030° C.
 18. Method according to claim 17, characterizedin that the metallic foil used to form the at least one metallic layer(12, 13) of the first type, before being bonded to the ceramic layer(11), is tempered in an inert atmosphere, for example a nitrogenatmosphere, by heating at a temperature below the process temperature ofthe direct bonding process.
 19. Method according to claim 17 or 18,characterized in that the application of the glass-containing paste andthe baking on of this paste is repeated at least one time in order toincrease the thickness of the at least one insulating layer made of theglass-containing material.
 20. Method according to one of the foregoingclaims, characterized in that the application and baking of the pasteforming the additional metallic layer of the second type (15, 15 c) isrepeated at least one time in order to increase the thickness of thisadditional metallic layer.
 21. Method according to one of the foregoingclaims, characterized in that a composite layer comprising at least twoinsulating layers (14) made of the glass-containing material and/or atleast two metallic layers (15, 15 c) of the second type is applied tothe at least one metallic layer (12) of the first type at least in onepartial area.
 22. Method according to one of the foregoing claims,characterized by the structuring of the at least one metallic layer (12)of the first type in order to form contact surfaces, mounting surfacesand/or strip conductors for at least one power area of the substrate.23. Method according to one of the foregoing claims, characterized bythe structuring of the at least one metallic layer of the second type inorder to form strip conductors, contact surfaces, mounting surfaces forat least one control or driver area of the substrate.
 24. Methodaccording to one of the foregoing claims, characterized in that severalsubstrates are produced multiply on one common ceramic plate forming theceramic layer (11).
 25. Method according to one of the foregoing claims,characterized in that a solder stop application or area (23) is formedon one partial area of the metallic layer (12), preferably on at leastone structured area (12′) of this metallic layer by application andbaking of the glass-containing paste.
 26. Method according to claim 25,characterized in that the application of the solder stop area takesplace together with the application of the insulating layer (14, 14 c).27. Module, produced using a metal-ceramic substrate according to one ofthe claims 1-14, characterized in that at least one exposed, structuredarea (II) of the metallic layer of the first type forms stripconductors, contact surfaces, mounting surfaces, etc. for at least onesemiconductor element (3, 4) provided there.
 28. Semiconductor moduleaccording to claim 27, characterized in that the at least one metalliclayer (15, 15 c) with structured areas (15′) forms strip conductors,contact surfaces and/or mounting surfaces for components (6) of at leastone driver or control stage.